This program focuses on the bioelectric characterization of developing mouse spermatozoa using separated spermatocytes, spermatids and immature spermatozoa. Membrane potential and membrane resistance of these differentiating cells will be measured with intracellular glass microelectrodes and will be related to the extracellular concentration of the ions--potassium, sodium, chloride--in order to determine the primary contributor to resting membrane potential. Concentration of potassium and chloride in the cells will be measured with ion-sensitive microelectrodes. The results will be analyzed using the Nernst and Goldman equations. Testis tubule fluid is potassium-dominated in some mammals; the sodium-potassium distribution reverses in the end-product-diluent, seminal plasma. The cell membrane permeability changes in the developing spermatozoon may temporally coincide with these variations in ion distribution. Both active and passive components of movements of ions will be analyzed using data from measurements of membrane potential, radioisotope determinations of fluxes of labelled potassium, sodium, chloride in the presence and absence of inhibitors of transport ATPase. Acquisition of motility at the level of the spermatid will be investigated by cinematography and related to the membrane properties in light of previously established membrane characteristics of the mature spermatozoon.